Hi,
I've attached some pics of my firewall. The aircraft is a fairly early 4, and had issues here when I first started flying it. 9 years ago I rebuilt it after it suffered a landing accident, using new engine mount, long legs, firewall, side panels and new style corner weldments.
The aircraft operates from a grass strip, and has not had a heavy landing; I'm the only pilot. Within weeks of the rebuild I could hear the firewall flex as I taxied, and just new what was going to happen!
It's now back in the workshop for instrument and radio upgrade, and I'll be doing the firewall as well.
Vans have suggested incorporating the gusset in the lower corners, and I'll be taking great care with alignments.
Does anyone have any other suggestions. I don't really want to do it again!
Thanks
PS. I'm disabled from posting photos. Could do pm's perhaps ? [ed. Upper left corner look for 'Inserting Pics' link. That's how to do it. v/r,dr]

Had those same marks on my -4 way back when...~3000hrs later, it's still going with no signs of distress. If I can recall correctly, this sort of wrinkling is visible on more than a few -4's.

Yes - those showed up after a not-so-smooth landing on grass.

I wouldn't worry about the wrinkles, but I would have a look at the fwd corners to make sure all is well - seems like that area might benefit from some additional interior parts to spread the loads around better. Seems that corner area might be a wee bit too flexible.

I would also add a 1/8" 4130 gussets to the lower attach tubes..

__________________Best,
Mark

"Not everyone needs a Rocket. Some folks, however, shouldn't live life without one.
You know who you are."
Budd Davisson, 1997

Very common. When I bought my plane, I saw that and the guy doing the pre-buy said not to worry. He's done many pre-buys and assured me they are present on almost half the RV4's he's seen. I had some gussets added to mine.

The loading at that point is complex with the back and outwards sweep of the legs, the twisting moment that the brakes have, torque from the prop and the weight of the motor. I've sat and looked at it for ages and still can't see how it happens!

The loading at that point is complex with the back and outwards sweep of the legs, the twisting moment that the brakes have, torque from the prop and the weight of the motor. I've sat and looked at it for ages and still can't see how it happens!

The Harmon and F1 use the same sort of setup, but none of those have any firewall wrinkles. I would say that fwd fuselage side skin should be .040, as is done in the larger, heavier examples. Might add some skin stiffeners too, since the HR and F1 fwd side skins are curved, which changes the equation.

__________________Best,
Mark

"Not everyone needs a Rocket. Some folks, however, shouldn't live life without one.
You know who you are."
Budd Davisson, 1997

My early '90s era -4 has firewall wrinkles. But no evidence of skin, attach point weldments, or aluminum structure damage. No detectable distortion to the airframe. The motor mount still aligns when removed/reattached.

Perhaps it's worth pointing out that the firewall is non-structural. If it's wrinkled, it obviously indicates further inspection is needed, but it isn't structural damage in and of itself.

My 1994 RV-4 has same wrinkle. It has been this way for years and many hours. I didn't build it, but it was this way when I bought it. The A&P/IA maintaining it for almost ten years said if had been that way and unchanged it that time. I've had a couple of other RV builders look and no one seems to think it is an issue. Everything else is straight and solid. The plane has just over 1000 hours TTAFE.

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